Datasheet LTC1043 (Analog Devices) - 7

LTC1043
U U W U APPLICATIO S I FOR ATIO
recover from the latch mode when the input drops 3V to 4V with an external clock to override the internal oscillator. below the voltage value which caused the latch. For Although standard 7400 series CMOS gates do not instance, if an external resistor of 200Ω is connected in guarantee CMOS levels with the current source and sink series with an input pin, the input can be taken 1.3V above requirements of Pin 16, they will in reality drive the Cosc the supply without latching the IC. The same applies for the pin. CMOS gates conforming to standard B series output C+ and C– pins. drive have the appropriate voltage levels and more than enough output current to simultaneously drive several
COSC Pin (16), Figure 6
LTC1043 COSC pins. The typical trip levels of the Schmitt The Cosc pin can be used with an external capacitor, Cosc, trigger (Figure 6) are given below. connected from Pin 16 to Pin 17, to modify the internal oscillator frequency. If Pin 16 is floating, the internal 24pF
SUPPLY TRIP LEVELS
capacitor, plus any external interpin capacitance, set the V+ = 5V, V– = 0V VH = 3.4VVL = 1.35V oscillator frequency around 190kHz with ±5V supply. The V+ = 10V, V– = 0V VH = 6.5VVL = 2.8V typical performance characteristics curves provide the V+ = 15V, V– = 0V VH = 9.5VVL = 4.1V necessary information to set the oscillator frequency for various power supply ranges. Pin 16 can also be driven 12 V+ = 15V 10 V– = 0V 8 V+ = 10V V– = 0V 6 1 OUTSIDE FOIL 4 V+ = 5V CS 2 CHARGE INJECTION (pCb) V– = 0V 2 3 0 0 2 4 6 8 10 12 14 16 PRINTED CIRCUIT LTC1043 V BOARD AREA IN (V) LTC1043 • AI05 LTC1043 • AI04
Figure 4. Individual Switch Charge Injection Figure 5. Printed Circuit Board Layout vs Input Voltage Showing Shielding the Sampling Capacitor
V+ 4 38µF COSC 16 TO CLK GENERATOR COSC 24pF (EXTERNAL) 17 V– (24pF) fOSC = 190kHz • (24pF + COSC) LTC1043 * AI06
Figure 6. Internal Oscillator
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